In a telephone system, incoming calls may be handled a number of different ways, depending on the particular type of customer premises equipment (CPE) that is being used. For example, mid- to large-size enterprises may have one or more private branch exchanges (PBX) installed on premises that receive incoming calls and that provide such functions as interactive voice response (IVR), voicemail, and/or automatic call forwarding. In some cases, particularly for small companies and entities for which it is impractical to purchase and install a PBX, some PBX-like services may be provided at the switch level by a telephone company. Such services, which are typically referred to as Centrex-type services, may mimic the operation of a PBX, and may provide advanced call handling capabilities, IVR, voicemail, and other features without the necessity of installing expensive equipment. Some advanced calling features, such as call forwarding, are provided by Advanced Intelligent Network (AIN) functionality that is included in some current telephone systems.
In addition to PBX and Centrex-based call handling, some advanced call handling functions may be provided by a Voice over IP (VoIP) internet telephony system. Currently, to provide Internet telephony communications to a subscriber, a subscriber must obtain equipment, such as Integrated Access Devices (IADs), Analog Terminal Adapters (ATAs), telephone adapters (TAs) and the like, to be installed at the subscriber's premises, for example, a customer's home. The equipment is needed to support a voice path within the premises and through the broadband connection, for example, a digital subscriber line (DSL) connection, back to the Internet Service Provider (ISP). Once the necessary equipment is installed, customers/subscribers can connect their existing analog phones, for example, Plain Old Telephone Service (POTS) phones, to the Analog Terminal Adaptors (ATAs) or telephone adapters (TAs) to originate and/or receive calls using Internet telephony, for example, over a VoIP line. A VoIP dial-tone is provided by the telephone adaptor (TA) to any phone extensions with ATAs connected. Incoming call processing may be performed at the customer premises or at a remote server with which the IAD communicates.
In addition to traditional PBX and Centrex-like services, VoIP systems provide users with certain functionality not typically available to users of traditional analog telephone services. For example, a user of a VoIP system may be able to customize incoming and outgoing call handling procedures, call preferences, call permissions, etc., using an IP interface to a feature server (application server). Call notifications may be provided to a user via instant messaging, and a user may be able to adjust call handling for an incoming call via an IP connection with the VoIP server without answering the call.